Self operating pressure actuated valve

ABSTRACT

1. A SELF OPERATING PRESSURE ACTUATED VALVE FOR CONTROLLING THE FLOW OF FLUID FROM A FIRST REGION TO A SECOND REGION WHICH COMPRISES: A. A BARRIER BETWEEN SAID FIRST AND SECOND REGIONS, SAID BARRIER HAVING AN OPENING THEREIN FOR THE PASSAGE OF FLUID, AND B. A POPPET CLOSURE FOR SAID OPENING, SAID POPPET BEING MOVEABLE TO OPEN OR CLOSE SAID OPENING IN RESPONSE TO PRESSURE, THE OPENING FORCE FOR SAID POPPET BEING THE EFFECT OF THE PRESSURE IN SAID SECOND REGION ACTING THROUGH SAID OPENING UPON A FIRST PORTION OF THE SURFACE OF SAID POPPET SAID OPENING FORCE BEING OPPOSED BY A CLOSING FORCE FROM THE EFFECT OF A SUBSTANTIALLY CONSTANT PRESSURE UPON A SECOND PORTION OF SAID POPPET, SAID SUBSTANTIALLY CONSTANT PRESSURE BEING LOWER THAN THE PRESSURE IN SAID FIRST REGION.

ttes tent [191 nit Lieberman et a1.

[ Dec. 3, 1974 [75] inventors: Seymour Lieberman, Los Angeles;

Joseph Michael Rice, Manhattan Beach, both of Calif.

[73] Assignee: Transtech, Manhattan Beach,

' Calif.

[22] Filed: Sept. 18, 1972 [21] Appl. No.2 289,872

52 U.S.Cl. 137/4s4.2,302/29 511 lnt.Cl. 865g 53/04 [58] FieldofSearch ..137/484.2,484.4,484.6,

Primary ExaminerHenry T. Klinksiek Assistant Examiner-Robert J. Miller Attorney, Agent, or Firm-Saul Epstein [57] ABSTRACT A self operating pressure actuated valve useful in air cushioned conveyor systems wherein the load is transported on a pallet which is supported on a cushion of air as well as in other applications. Back pressure on the valve acts on the poppet closure to open the valve when the back pressure on the poppet reaches a pre determined level. Means are provided to allow the valve closing force to be higher than the valve opening force, if desired. In an air cushioned conveyor system the valve detects the presence of the load carrying pallet by sensing the pressure field due to the pallet air cushion. The air cushion pressure causes the valve to open and pressurized air from a manifold under the sure on it.

15 Claims, 6 Drawing Figures PATENIELDEB 31914 SBEEJZBFZ F POPPET Po ,5 7" Pas/770M a Am M ii m w llpa M M P 0 W O a m w w 1 SELF OPERATING PRESSURE ACTUATED VALVE BACKGROUND OF THE- INVENTION 1. Field of the Invention This invention relates to valves and more particularly toself actuating valves which open when the back pressure on the valve increases to some predetermined level.

.2. Prior Art Pressure actuated valves sensitive to back pressure have been described in previous patents, e.g. 3,251,595, 3,081,886, and 3,279,863, but in general the valves have been complicated and expensive to make. The use of intricate closures such as sleeve valves and separate operators for the valve rather than having the valve mechanism itself be sensitive to the back pressure have contributed to the complication and expense. Also, the moving mass of prior art valves is, in general, high leading to poor dynamic response. Another drawback of many of the prior art valves is the inordinate air capacity requirements for startup in order to initially close the valves.

The present invention overcomes all of these disadvantages, providing an extremely light moving mass for dynamic response, and a simple inexpensive to fabricate poppet valve mechanism requiring-no external operators. Means are also provided which allow a valve to be designed with negative hysteresis so that small changes in pressure will open or close the valve thus providing a valve which will respond rapidly to a demand for air and will also close rapidly when the demand is removed. This feature allows a system to be constructed with a smaller air supply system since considerably less air is consumed than systems using prior art valves.

SUMMARY OF THE INVENTION Air cushioned conveyor systems are similar in principle to the familiar ground effect machine wherein the machine is floated on a cushion of compressed gas. By maintaining the pressure of the gas under the device at a sufficiently high pressure, the weight of the load can be overcome and the device will float independent of any physical support. Once floating, the device can be moved horizontally essentially without friction. .Compressed gas can be maintained under the device either by carrying a compressor on the vehicle or by providing a track which supplies compressed gas from below. Typical systems operate on pressures of from a few inches of water to a few psi, the pressure being determined primarily by the maximum load to be transported. For example if a load of 1500 pounds were to be transported on a vehicle having a support platform or plenum facing the track of 1.5 X 3 feet or 4.5 square feet, the pressure required to float the device would be 333 pounds per square foot or about 2.3 psi. A supply pressure somewhat higher than this would have to be used in a practical conveyor 'system since leakage around the edges of the support area will tend to reduce the actual pressure supporting the load.

This invention is concerned with a valve for installation in a track to control the flow of gas for support of such a vehicle. The valve senses the presence of a vehicle approaching or above it and automatically opens allowing compressed gas from a manifold under the track to maintain the support cushion under the vehi- A plurality of valves spaced along the track provides a continuous source of compressed gas to make up leakage losses and maintain flotation of the vehicle over its journey.

The valve of this invention detects the presence of a vehicle by sensing the increase in pressure on the track exerted by the cushion of gas supporting the vehicle. The area of the valve poppet exposed to the track is such that a small increase in gas pressure on the track caused by the covering of the valve by a vehicle floating on a gas cushion will cause the net force on the poppet to be "such that the valve will open. Conversely, when the valve is uncovered, the net force on the poppet will reverse causing the valve to reclose.

During the time the valve is open, gas is continually flowing from the manifold under the track to the plenum under the load to make up any gas which leaks out from around the periphery of the plenum. This gas increases in velocity as it passes the valve opening and is thus reduced in pressure in accordance with Bernoullis theorem. This low pressure region acts on the poppet in such fashion as to cause the closing pressure of the valve to be higher than the opening pressure. This negative hysteresis" effect allows a valve to be designed which is extremely sensitive to both the approach and departure of the vehicle.

Deflector vanes located in the throat of the valve impart a component of velocity to the flowing gas which is parallel to the track. By orienting the vanes in the desired direction, the propulsion component of velocity parallel to the track will cause the vehicle to be accelerated or braked.

It is accordingly an object of this invention to provide a simple inexpensive self operating valve sensitive to back pressure.

It is a further object to provide such a valve with improved response characteristics.

Yet another object of this invention is to provide a valve with negative hysteresis characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cutaway perspective view of an air cushioned conveyor system showing a plurality of the valves of this invention installed therein.

FIG. 2 is a cross section taken at 2-2 of FIG. 1 showing a cross section of the presently preferred embodiment of the invention in the closed position.

FIG. 3 is a cross sectional view of the present invention in the open position.

FIG. 4 is a graph of the pressure-position characteristics of the presently preferred embodiment of the invention.

FIG. 5 is a partial cross sectional view of the valve of this invention indicating the various areas which contribute to its operation.

FIG. 6 is a cross sectional view of a second preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1 where a plurality of the self actuating valves of this invention are shown installed in an air cushioned carrier system. The system shown comprises a track made up of manifold module sections 11, I2, and 13 which are fastened together so as to form a flat top surface plate 16. The manifold module sections 11, 12, and 13 are pressurized by a blower which is not illustrated and, in the absence of anything covering the valves, the valves are closed preventing the pressurizing gas from escaping.

It has been found convenient in manufacturing air cushioned conveyor systems to construct the manifold sections in modular sizes and to assemble the complete system from such modules. For example, a typical manifold module may be 6 inches high by 6 inches wide by 10 feet long. Valves having throats approximately 3 inches in diameter may be spaced along the manifold section on approximately 6 inch centers. Three such modular sections are shown in FIG. 1 making a track 18 inches wide. As many 10 foot lengths as are desired may be joined together to make the track the desired length. The load is carried on pallet 17 which floats on a gas cushion just above surface 16 and is thus free to move along the track without friction. Side rails 14 and 15 keep the pallet on the track during its journey from one end of the track to the other.

The gas forming the gas cushion is supplied from the manifolds through valves 10 which sense the presence of the pallet and open automatically supplying the gas on which the pallet 17 rides. As the pallet 17 proceeds on its trip along the track, new valves 10 are constantly being first covered and then uncovered by the pallet as it passes, the valves under the pallet at any instant being open and all others being closed.

A cross section of the presently preferred embodiment of the valve of this invention is shown in FIG. 2 installed in a typical manifold section 13. The manifold section contains a plurality of holes 22 in the top surface plate 16 of the manifold section and corresponding concentric holes 32 in the bottom surface 18 to receive the valves 10. The valve is supported by mounting ring 20 and is fastened to top surface 16 by screws 21. Top surface 16 is preferably dimpled around hole 22 so that mounting ring 20 is flush with surface 16. Mounting ring 20 is formed so that it has a U shaped cross section, one leg being screwed to surface 16 by screws 21 and the other forming valve seat 23.

Brackets 24, welded to mounting ring 20 support tube 25 concentric with mounting ring 20 and spaced from it. The bottom of tube 25 protrudes through hole 32 in the bottom 18 of the manifold and soft gasket 26 seals the joint so'that valve '10 will seat properly on the top surface 16 even though there is some misalignment between hole 22 and hole 32'.

The valve poppet is comprised of a plastic or aluminum disc 28 covered with a flexible boot 27 which has the form of a single convolution bellows and is made of a suitable elastomer. A boot with a plurality of convolutions would, of course, accomplish the same result as a single convolution boot. The boot 27 has a small bead 29 on its top surface near the periphery. The valve seals at the point bead 29 contacts valve seat 23. The location of bead 29 has an effect on the valve characteristics as will be explained later, however, it should be understood that a valve within the spirit of this invention can be made without a bead 29 so that a seal is made over the entire surface of valve seat 23.

The open end of the bottom is stretched over the end of tube 25 making a seal at that point. With the poppet up against seat 23 as shown in FIG. 2 the valve is closed and pressurized gas in the manifold section is prevented from escaping. When the poppet is down against the top of tube 25, gas may flow out of the manifold through the opening between valve seat 23 and the poppet 30 as indicated by the arrows in FIG. 3.

Inside of mounting ring 20 is deflector ring 40 which is free to rotate but is kept from separating from the mounting ring 20 by bead 41. Attached to the deflector ring 40 are deflector vanes 42. The gas flowing through the valve is given a component of velocity in the plane of the track by the deflector vanes and by rotating the deflector ring 40 to the proper position an accelerating or braking force can be imparted to the pallet. Side ways forces to aid in turns can also be achieved.

The valve of the present invention can be made either normally open or normally closed, that is the static position of the valve with atmospheric pressure on all parts can either be open or closed. If the boot 27 is molded of a thin elastomer which is essentially limp, the weight of disc 28 will cause the poppet 30 to rest on the top of tube 25 thus creating a normally open valve. If, on the other hand, the convolution of boot 27 is relatively heavy, having some spring effect and the convolution is molded in an extended position, the disc 28 will be held up against seat 23 by the spring action of the boot 27 and the valve will be normally closed. It will be realized by those skilled in the art that an auxiliary spring bearing up on disc 28 will also result in a normally closed valve.

The operation of the valve in use is the same whether it is of the normally open or the normally closed variety, however, a system using normally open valves requires extra air capacity in order to close the valves on start up of the system. When the system is initially pressurized, gas will escape from open valves preventing pressure from building up in the manifold sections and the system will not become operational until the valves are closed.

If sufficient fan capacity is provided, or if portions of the manifold can be blocked off for start up so that only a few valves at a time are pressurized, the valves will close due to unbalanced pressure on the poppet caused by the flow of escaping gas.

In FIG. 3, if pallet 17 were not present, gas at essentially atmospheric pressure would flow out of manifold chamber 13 through the space between valve seat 23 and poppet 30 and escape to atmosphere through deflector ring 40. The interior of tube 25 is at atmospheric pressure so that, except for flow effects all parts of the system are at atmospheric pressure. However, due to the higher velocity of flow as the gas passes valve seat 23, its pressure drops and when the pressure drop due to flow times the area of the valve seat is sufficient to overcome the weight of poppet 30, the poppet will rise and the valve will close. The pressure in the manifold will of course build up somewhat during the start up process and the effect of pressure on the under side of poppet 30 in the area on which it acts will assist the closing action. When all valves are closed, the pressure in the manifold will build up to operating pressure and the system is ready for operation. The reduced pressure due to flow in the flow channel formed by the outer portion of poppet 30 and valve seat 23 when the valve is open has other beneficial effects which will be described presently.

If valves of the normally closed variety are used, no gas will escape on initial pressurization and the system will be ready for operation as soon as pressure has built up in the manifold.

If a pallet is placed on a pressurized manifold, it will rest on the top surface of the manifold and not float since there is no pressurized gas under the pallet to cause the valves to open. However, a small leak may be provided in the top 16 of the manifold or the valve itself can be made with an imperfect seat 23 so to provide air for initial pressurization of a pallet placed on the track.

When the gas under the pallet builds up to the point that its pressure times the area of the pallet equals the load on the pallet, the pallet will begin to rise, and gas will leak'out to atmosphere from around the periphery of the pallet and the pallet will assume some equilibrium position above the manifold top surface 16 which allows the same amount of gas to leak out around the periphery of the pallet as is being supplied to its underside. At the same time that pressure is building up under the pallet tending to float it, the forces acting downward on the poppets of the valves under the pallet are increasing, and at some preset level of pressure the valves will open resulting in a rapid increase in pressure to the equilibrium value, which just balances the load on the pallet.

FIG. 4 diagrams the position of the valve poppet as a function of the pressure under the pallet, P,,. This figure is best understood if viewed in conjunction with FIG. 5 which illustrates the various areas of poppet 30 whichare subjected to the pressures which cause the valve to actuate. For purposes of explanation all pressures are expressed in gage pressure units.

A the area of the top of poppet 30 within the throat of deflector ring 40. A the annular area outside of the throat of deflector ring but inside of sealing bead 29.

A the area of the top of the poppet outside of sealing bead 29. v

A, the effective area on the underside of the poppet on which the manifold pressure, P,,,, acts, that is, an area which is numerically equal to the upward force on poppet 30 due to a unit increase in pressure in the convolution of boot 27 and on the underside of the lip of the poppet which overhangs the convolution. The effective Area A, is somewhat less than thephysieal area indicated in FIG. 5.

P,,, the manifold pressure.

P the-pressure existing on the track over the valve.

F,,,,,,,,.,, the net force acting upward on the poppet due to pneumatic pressures acting on the valve. When the valve is closed and no pallet is covering the throat of the valve, P,,=0 and the valve is in the condition indicated as point 50 in FIG. 4. The force on the poppet is:

popml m 4 3) By making A slightly smaller than A,, the valve will be held closed since F will be positive, but only a small downward pressure on the poppet will be required to open the valve. The magnitude of the pressure required can be selected by proper adjustment of the areas A and A As a pallet moves across the mouth of the valve, the air cushion under it increases the pressure P on the poppet Areas A and A until P,,,, is reached (point 51). This is the point at which F =0 and the valve starts to open. The forces on the poppet at this point are:

It can be seen that P,, at the point of opening can be made as small as desired by adjustment of the area A, and A As the valve opens P increases rapidly due to the flow of gas from the manifold through the open valve into the mouth of the valve and an equilibrium pressure is established at some pressures less than P,,,. The equilibrium pressure will be less than P,,, because gas will continue to flow to supply losses around the pallet and there will be a head loss across the valve opening A and A;,. This condition is indicated as point 52 in FIG. 4.

Gas will continue to flow out ofthe manifold to maintain the pallet floating and supply the losses so long as the valve remains covered by the pallet.

As the pallet continues on its journey and the valve is uncovered, the pressure P, drops until P,,,, (point 53) is reached. At this point F 0 and the pressures existing are:

F O P,,, xA, P,,xA P,(A +A where P, is the pressure existing in the area between the poppet 30 and valve seat 23. Since the gas flowing in this area has a higher velocity than that on either side of the valve seat, Bernoullis theorem indicates that P; is less than either P,,, or P,,. A comparison of this equation with the one previously given for the conditions existing at P,,,,,.,,,-,,,, shows that F occurs at a higher value of P,, than P,,,,,.,,,-,,,,. This negative hysteresis characteristic makes the valve of this invention very sensitive and rapidly operating and a valve which holds gas losses to a minimum. The desirability of a negative hysteresis loop is readily appreciated by those skilled in the art. With such a characteristic the valve can be made very sensitive to an approaching pallet, opening rapidly so as to provide smooth system operation and yet the valve can be made to close when the receding pallet just begins to uncover the valve so as to prevent excessive gas leakage to the atmosphere.

The factors which influence the width of the hysteresis loop", that is the difference in pressure between P,,,, and Pmmng are, of course A and A and also the amount of poppet travel. The smaller the valve opening, the higher is the velocity of the gas in areas A and A and therefore the lower is P, and thus the higher is elosinrr We have found that a length of the flow channel between the poppet and the valve seat approximately equal to the separation of the poppet from the valve seat when the valve is open results in a substantial and useful width of the hysteresis loop. A longer channel, relatively, would result in even greater effect.

The fact that the P,.,,, is greater than P,,,,,.,,,,,,, means that thevalve is unstable in the region P,,,,,.,,,,,,, P,, P can, and the valve will tend to chatter if P,, is maintained in this region. However, in actual use P, will increase as the valve is covered and decrease rapidly as the valve is uncovered so that there is little possibility that the unstable condition will persist long enough to create a problem.

The foregoing explanation of the operation of the valve does not take into consideration the weight of the poppet or the effects of any spring bias introduced by elasticity of the boot 27 or a separate bias spring open ating on the poppet. It will be clear to those skilled in the art how these items affect the operating points of the valve and omitting them facilitates explanation.

The disc 28 is preferably made of plastic or other lightsubstance and the boot 27 is also made lightweight in order to keep the moving mass light and therefore minimize inertial effects.

Deflector vanes 42 are set into ring 40 on an angle so as to impart a velocity component to the flowing gas along the surface of the track. The underside of pallet 17 may be divided into a plurality of sections by dividers 61 upon which the gas flowing out of the manifold impinges, thereby imparting forward motion to the pallet. The deflector ring 40 is free to turn inside mounting ring and may be either controlled or set locked in a desired orientation. Valves located near the end of the track can have their deflector rings turned to provide a braking effect on the pallet, which will bring it to a smooth stop at the end of its journey. Turning the deflector vanes sideways will facilitate the change in direction occurring at turns in the track.

A second preferred embodiment of this invention is illustrated in FIG. 6. This embodiment is the same in all respects as the first embodiment, previously explained, with the exception of the construction of the valve poppet. The poppet 70 is comprised of a disc 71 attached to a tube 72 which is a sliding fit in tube 25. The length of tube 72 and the closeness of its flt into tube keep the leakage from the manifold into tube 25 down to a reasonably low level. Boot 73 containing sealing bead 74 on its upper surface covers the top surface of disc 71 and extends over the edge so as to retain the boot on the disc.

If a normally closed valve is desired, ring 75, welded to tube 25 will support the bottom end of spring 76 which biases the poppet 70 closed. This spring bias is optional and if omitted, a normally open valve results.

The operation of this embodiment is the same as previously explained for the first embodiment.

What has been described is a novel self operating pressure actuated valve installed in an air cushioned conveyor system. It will be clear to those skilled in the art that the valve of the present invention has uses in other applications than that described. It is useful in applications involving air or other fluid mediums and the illustrative use of the valve in an air cushioned conveyor system should not be taken as narrowing the scope of the invention. Various modifications will occur to those skilled in the art which will fall within the scope and spirit of the appended claims.

We claim:

1. A self operating pressure actuated valve for controlling the flow of fluid from a first region to a second region which comprises:

a. a barrier between said first and second regions,

said barrier having an opening therein for the passage of fluid; and g b. a poppet closure for said opening, said poppet being moveable'to open or close said opening in response to pressure, the opening force for said poppet being the effect of the pressure in said second region acting through said opening upon a first portion of the surface of said poppet said opening force being opposed by a closing force from the effect ofa substantially constant pressure upon a second portion of said poppet, said substantially constant pressure being lower than the pressure in said first region.

2. A self operating pressure actuated valve for controlling the flow of fluid from a first region to a second region which comprises:

a. a barrier between said first and second regions, said barrier having an opening therein for the pars sage of fluid;

b. a poppet closure for said opening, said poppet being moveable to open or close said opening in response to pressure, the opening force for said poppet being the effect of the pressure in said second region upon a first portion of the surface of said poppet, said opening force being opposed by a closing force from the effect of a substantially constant pressure upon a second portion of said poppet, said substantially constant pressure being lower than the pressure in said first region; and

c. means for reducing the pressure on a portion of the area of said poppet exposed to flowing fluid, said pressure reduction operating on said poppet in a direction tending to close said valve whereby a negative hysteresis effect is attained.

3. A self operating pressure actuated valve as recited in claim 2 wherein said means for reducing pressure is a flow channel, a portion of said poppet being one wall of said flow channel whereby fluid flowng through said channel has a higher velocity than fluid on either side of said channel. 1

4. A self operating pressure actuated valve for controlling the flow of fluid from a first region to a second region which comprises:

a. a barrier between said first and second regions,

said barrier having an opening therein for the passage of fluid; and

b. a poppet closure for said opening, said poppet having a pair of opposed faces and being moveable to open or close said opening in response to pressure, the opening force for said poppet being the effect of the pressure in said second region upon a first portion of the surface of said poppet, said opening force being opposed by a closing force from the effect of a substantially constant pressure upon a second portion of said poppet, said substantially constant pressure being lower than the pressure in said first region, said first portion of the surface of said poppet being at least a portion of the first of said faces, and said second portion of the surface of said poppet being at least a portion ofthe second of said faces, whereby an increase in pressure in said second region will cause said valve to open.

5. A self operating pressure actuated valve as recited in claim 4 and further including force generating means responsive to the pressure in said first region, said force generating means acting on said poppet in a direction tending to close said valve.

6. A self operating pressure actuated valve as recited in claim 5 wherein said force generating means is a third portion of the surface of said poppet, said third portion of the surface of said poppet being a portion of said second face.

7. A self operating pressure actuated valve as recited in claim 6 wherein said second and said third portions of said poppet are separated by a flexible divider, said divider preventing pressure on said third portion from reaching said second portion.

8. A self operating pressure actuated valve as recited in claim 7 wherein a portion of said first face is in a spaced parallel relationship to a portion of said barrier when said valve is open forming a flow channel whereby a low pressure region is created in said flow channel by the increase in velocity of fluid flowing out of said first region through said channel.

9. A self operating pressure actuated valve as recited in claim 8 and further including elastic means operating in a direction tending to close said valve.

10. A self operating pressure actuated valve as recited in claim 7 and further including means for reducing the pressure on a portion of the area of said poppet exposed to flowing fluid, said pressure reduction operating on said poppet in a direction tending to close said valve whereby a negative hysteresis effect is attained.

11. A self operating pressure actuated valve as recited in claim 10 wherein said means for reducing pressure is a flow channel, a portion of said poppet being one wall of said flow channel whereby fluid flowing through said channel has a higher velocity than fluid on either side of said channel.

12. A self operating pressure actuated valve comprising:

a. a manifold having a substantially flat horizontal top surface, said manifold being adapted to being pressurized and said top surface having an opening for the passage of air therein;

b. a valve seat within said manifold and surrounding said opening;

c. a poppet closure for said valve seat, said valve seat being so disposed with respect to said top surface that pressurized fluid within said manifold cannot escape through said opening when said poppet is against said valve seat;

d. a hollow support tube mounted within said manifold for supporting said poppet, the interior of said support tube being vented to atmosphere; and

e. a flexible boot extending between said poppet and said support tube, said boot sealing the gap be tween said poppet and said support tube whereby pressurized fluid within said manifold cannot enter said support tube, said flexible boot allowing said poppet to move in response to pressure differential across said poppet to either rest against said valve seat thereby closing said valve or be away from said valve seat thereby opening said valve.

13. A self operating pressure actuated valve as re cited in claim 12 wherein a flow channel parallel to said top surface is formed between said poppet and said valve seat when said valve is in an open position whereby the velocity of fluid in said channel is higher than the velocity on either side of said channel creating a reduced pressure, said reduced pressure acting on said poppet in a direction tending to close said valve.

14. A self operating pressure actuated valve as recited in claim 13 wherein said flow channel is at least as long as its width.

15. A self operating pressure actuated valve as recited in claim 14 and further including a plurality of deflector vanes positioned in said opening, said deflector vanes imparting a component of velocity parallel to said top surface to fluid emanating from said valve. 

